Flash lamp



Dec. 13, 1955 M. PIPKIN 2,

FLASH LAMP Filed Oct. 50, 1951 I s 9 i 9 Inventor: Marvin PipKin,

His Attorney.

FLASH LAMP Marvin Pipkin, Cleveland Heights, Ohio, assignor to GeneralElectric Company, a corporation of New York Application October 30,1951, Serial No. 253,770

7 Claims. (CI. 6731) My invention relates to flash lamps in general andto a method of manufacture thereof, and more particularly to a flashlamp having means therein adapted, upon leakage of atmospheric air intothe lamp envelope, to either provide a visible indication of thedefective character of the lamp or render the lamp inoperative, or both.

Flash lamps of the general type in use at present comprise ahermetically sealed glass envelope containing a light-giving charge anda combustion-supporting gaseous filling at a pressure less thanatmospheric. When flashed, the light-giving charge reacts with thegaseous filling to produce a momentary flash of light of high intensitysuitable for photographic purposes. If the envelope of the flash lampremains in its hermetically sealed condition at the time of flashing ofthe lamp, the reaction proceeds in proper manner and in safety, withoutdanger of lamp explosion. However, if the hermetic seal of the envelopeis defective for some reason, as by the occurrence of a crack in theglass wall thereof, the leakage of atmospheric air into the envelopedilutes the gas filling and raises the internal gas pressure to a degreesuch as might result, depending on the type of lamp, either in poorlight output or in a violent explosion of the envelope on flashing ofthe lamp, with resultant danger of flying glass and injury to persons inthe immediate vicinity.

It is an object of my invention, therefore, to provide a flash lamphaving means for providing a visible indication as to whether or not thelamp envelope is in a hermetically sealed condition andthe lamp in aproper or a safe condition for use.

Another object of my invention is to provide a flash lamp having visiblemeans within the envelope thereof for indicating the leakage ofatmospheric air thereinto by the absorption of the moisture in such air.

Still another object of my invention is to provide a flash lamp havingmeans therein for rendering the lamp substantially inoperative uponleakage of atmospheric air into the envelope thereof.

A further object of my invention is to provide a method of making aflash lamp having an indicating and/or an inactivating means of theabove-mentioned character.

According to one aspect of the invention, the-envelope of a flash lampis provided interiorly thereof with a small quantity of a substance, inan anhydrous state, which is highly deliquescent and which willchangeits appearance upon absorption of the moisture present inatmospheric air leaking into the lamp envelope. Preferably, thesubstance is in the form of a coating located on the press portion ofthe re-entrant-glass stem of the lamp.

According to another aspect of the invention, the flash lamp may befurther provided with a coating of such a deliquescent substance on thebeads of combustible fulminating material which are customarily providedon the inner lead-in wires of the lamp in contact with the ignitionfilament connected thereacross, which coating, upon absorption ofmoisture from atmospheric air leaking into United States Patent the lampenvelope, will wet the fulminating material to 2,726,527 Patented Dec.13, 1955 2 a degree sufricient to render the lamp substantiallyinoperative.

Further objects and advantages of my invention will appear from thefollowing detailed description of a species thereof and from theaccompanying drawing which is an elevation of a flash lamp according tothe invention.

While in the drawing I have shown the invention as applied to a flashlamp of the so-called primer type disclosed and claimed in U. S, Patent2,291,983, M. Pipkin, in which the sole source of actinic light isconstituted by beads of a fulminating or primer material located withinthe envelope, it is to be understood that the invention is alsoapplicable to other flash lamps such as those wherein the source ofactinic light is constituted by a filling of combustible material in theform of wire, shredded foil or leaf foil.

Referring to the drawing, the flash lamp there shown comprises ahermetically sealed envelope or bulb 1 of a suitable light-transmittingmaterial such as glass and having a neck portion 2 to which is suitablysecured a conventional type base 3, as by cementing for instance. Thebulb 1 is filled with a combustion-supporting gaseous lling such asoxygen at a suitable pressure, preferably less than atmospheric, forinstance from mm. of mercury up to a pressure approximating oneatmosphere. In the particular primer-type lamp illustrated, the gasfilling comprises oxygen at a pressure of approximately mm. of mercury.The bulb is coated on its inner or outer surface, preferably on bothsurfaces, with a coating of a suitable light-transmitting lacquer orvarnish to thereby minimize cracking of the bulb on charge flashing andto render the bulb substantially shatterproof.

Sealed into the 'bulb 1 and extending thereinto from the neck portion 2thereof is a mount structure comprising a re-entrant stem 4 having apair of leading-in wires 5, 5 sealed into the press portion 6 of thestem and extending therethrough to the terminals of the base 3. Theleading-in wires 5, 5 are provided with juxtapositioned parallel innerlead portions 7, 7 across the inner ends of which is connected a smallignition filament 8 consisting of a straight length of wire of asuitable refractory metal such as tungsten. Mounted on the inner ends ofthe leading-in wires 5, 5, and at least partly embedding the filament 8,are beads or coatings 9, 9 of a suitable primer or fulminating materialsuch as disclosed in the aforesaid Patent 2,291,983, the said substanceconstituting the sole source of actinic light generated by the lamp. Thelight-giving material 9 preferably consists of a mixture of zirconiummetal powder, potassium perchlorate powder and sodium chlorate powderbonded together by a suitable binder such as nitrocellulose.

In accordance with the invention, the lamp envelope 1 is provided, at areadily visible location interiorly thereof, with a small quantity 10 ofone or more substances, in an anhydrous state, which are deliquescent-(i. e., which become liquid by absorption of moisture from thesurrounding atmosphere) and which undergo a change in their appearanceupon transformation from their anhydrous (solid) to their hydrated(liqudi) state. Upon leakage of atmospheric air into the envelope, suchas occurs when a crack develops in the glass wall of the envelope, theanhydrous substance 10 absorbs the moisture which is present in the airwhich has thus penetrated into the envelope, and undergoes atransformation in its appearance which provides a visible indication tothe user that the lamp is defective or in an unsafe condition to use.

The indicator substance 10 is preferably located with- .in the envelope1 at a point adjacent the neck 2 thereof where it will be exposed to theheat utilized to seal the mount into the envelope neck, such heatserving to expel the water of hydration from the substance 10 andtransform it into its anhydrous state. Also, the indicator substance 10is preferably located on a part of the lamp, such as the stem press 6 asshown, other than the inner wall of the envelope 1 for the reasorrthatthe inside lacquer coating with which the inside wall of the envelope iscustomarily provided prevents the substance 10 from readily absorbingmoisture whenlplaced on such a lacquered inside wall. 7

There are a number of materials known as hydrates which are suitable foruse as indicator substances 10 according to the invention, the onlyrequirements being that they be of a highly deliquescent character andthat when once placed in their dehydrated or partially dehydrated solidstate they not only absorb moisture readily upon exposure thereto andbecome transformed into a partially or completely hydrated liquid state,but in doing so they also undergo a change in their appearance. Examplesof deliquescent hydrates which may be satisfactorily utilized as theindicator material 10 are lithium bromide, lithium perchlorate, lithiumchloride, lithium nitrate, strontium perchlorate, copper sulphate orchloride, cobalt chloride, nickel chloride, nickel bromide and sodiumnitrate.

Of the various deliquescent hydrates suitable for the purposes of theinvention, it is preferable to employ a deliquescent hydrate of the typewhich, when in its partially or completely dehydrated state, is in theform of a readily visible powder of spongy or foam-like appearance andfor that reason will absorb moisture more readily and quickly uponexposure thereto and transform itself into a liquid state. In addition,it is also preferable to employ a deliquescent hydrate which is ashygroscopically sensitive as possible to effectthe desired appearancechange therein, i. e., one that requires the smallest amount of moistureabsorption to effect its appearance transformation and therefore will beeffective to indicate the presence of water vapor even when present inminute amounts. For such reasons, therefore, it is preferred to employ adeliquescent hydrate such as lithium bromide or strontium perchlorate,each of which possesses the above-described properties. Lithium bromide,however, has been found to be the most suitable material up to thepresent because even if it should be heated to an excessive temperatureduring the heating thereof to effect its dehydration, it neverthelessstill retains its capacity to readily absorb moisture and undergo atransformation in its appearance.

To produce a flash lamp according to the invention provided with avisible indicator means such as described above, a small quantity of asaturated solution of a suitable deliquescent hydrate, such as lithiumbromide for example, is placed on the press portion 6 of the glass stem4 of the lamp mount, and the latter then sealed into the envelope 1. Theheat of sealing is conducted through the glass stem to the press portion6 and causes the water of hydration in the indicator substance to beevaporated therefrom and the residue (anhydrous lithium bromide in thiscase) to assume a highly porous, foamlike, white appearance which isreadily visible. The envelope 1 is then immediately exhausted and filledwith oxygen or other combustion-supporting gas to the desired pressurethrough the conventional exhaust tube 11 which is then tipped-off tohermetically seal the envelope while the indicator substance 10 is stillin its dehydrated state. As long as the lamp envelope 1 remainshermetically sealed, the anhydrous lithium bromide retains its whitespongy appearance. However, .if a crack develops in the glass envelope1, the anhydrous lithium bromide 10 readily absorbs the moisture carriedinto the envelope by the atmospheric air penetrating thereinto, therebycausing its white appearance to disappear and the'material to turn waterclear, thus indicating the defectiveness of the lamp.

In order to render it as sensitive as possible, the indicator substance10 preferably'is only partially dehydrated.

only enough of its water of hydration being expelled to eflect atransformation in its appearance. By only partially dehydrating it tothe point where it first attains its transformed anhydrous appearance,the indicator substance 10 does not need to absorb as much moisture totransform itself back to its hydrous condition as it normally would ifit were excessively or completely dehydrated. Also, as small a quantityas possible of the indicator substance 10 is employed while stillproviding a readily visible deposit, in order to minimize the amount ofmoisture required to be present in the lamp envelope and absorbed by theindicator substance to transform it into its hydrated state, therebyrendering the indicator substance 10 as sensitive as possible.

As an alternative to the indicator means 10, but preferably in additionthereto, the flash lamp according to the invention may be provided withan inactivating means for rendering the flash lamp substantiallyinoperative upon leakage of atmospheric air into the lamp envelope 1.For this purpose the primer or fulminating beads 9 of the lamp are eachcoated with a layer 12 of a deliquescent substance such as that employedfor the indicator means 10. Upon leakage of atmospheric air into theenvelope 1, the deliquescent coatings 12 on the primer heads 9 absorbthe moisture in the air and change into a solution which then wets thematerial of which the primer beads are made, thereby rendering themsubstantially incapable of combustion or, in any event, retarding theircoinbustion to a degree sufficient to negative any possibility of thelamp exploding when operated, or flashing with the requisite speed toproduce the normal light flash. As long as the lamp envelope 1 remainssealed to the atmosphere, however, the coatings 12 on the primer beads 9remain in their dehydrated state and do not adversely affect thecombustion characteristics thereof in any objectionable manner. Thus,the lamp will possess substantially the same light-flash characteristicswhich it normally would possess if it were not provided with thecoatings 12 on the primer beads 9.

The coatings 12 of deliquescent material may be con veniently applied tothe primer beads 9 in any suitable manner, preferably by dipping thelamp mount, filament end first, into a saturated solution of thedeliquescent substance to a depth sufiicient to coat not only the primerheads 9 but also the inner leads 7 and at least a part of the stem press6 as well. In this manner both the lamp inactivating coatings 12 and theindicator coating 10 are applied simultaneously to the lamp mount. Also,if desired, the inner leads 7 may be coated with a layer of thedeliquescent material prior to the application of the primer beadsthereto. The dipping operation may be automatically performed on thesame apparatus customarily employed to automatically apply the primerbeads 9 themselves to'the lamp mount, such an apparatus being shown inFlaws patent 2,449,648, dated September 21, 1948. After the applicationof the coatings 16 and 12 to the lamp mount, the latter is then sealedinto the lamp envelope 1 and the coatings 10 and 12 properly dehydratedby the heat of the sealing operation as before, whereupon the lampenvelope 1 is immediately exhausted and gas-filled and then tipped-offto hermetically seal it while the deliquescent coatings 10 and 12 arestill in their dehydrated state.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A fiashlamp comprising a hermetically sealed lighttransmittingenvelope interiorly free of moisture, a lamp mount structure sealed insaid envelope, a light-giving charge in said envelope, acombustion-supporting gaseous filling in said envelope, and a quantityof a deliquescent substance in an anhydrous solid state located in saidenvelope on said mount structure, said substance being changeable inappearance and physical structure from its said solid state to a liquidstate upon exposure to and absorption of moisture entering theenvelope.

2. A flash lamp comprising a hermetically sealed lighttransmittingenvelope interiorly free of moisture, combustible means in said envelopecomprising a bead of fulminating material, a combustion-supportinggaseous filling in said envelope, and a coating of a deliquescentsubstance in an anhydrous solid state on said bead of fulminatingmaterial.

3. A flash lamp comprising a hermetically sealed lighttransmittingenvelope interiorly free of moisture and provided with a re-entrant stemhaving a press portion, a pair of lead-in Wires sealed through saidpress portion, ignition means in said envelope comprising a filamentconnected across said lead-in wires, a light-giving charge in saidenvelope, a combustion-supporting gaseous filling in said envelope, anda coating of a deliquescent substance in an anhydrous solid state onsaid stem press portion, said substance being changeable in appearanceand physical structure from its said solid state to a liquid state uponexposure to and absorption of moisture entering the envelope.

4. A flash lamp comprising a hermetically sealed lighttransmittingenvelope interiorly free of moisture and provided with a re-entrant stemhaving a press portion, a pair of lead-in Wires sealed through saidpress portion, ignition means in said envelope comprising a filamentconnected across said lead-in wires, a bead of fulminating materiallocated on each of said lead-in wires and at least partially embeddingsaid filament, a combustionsupporting gaseous filling in said envelope,and coatings of deliquescent substances in an anhydrous solid state onsaid stem press portion and on each of said beads of fulminatingmaterial, the deliquescent substance on said stem press being changeablein appearance and physical structure from its said solid state to aliquid state upon exposure to and absorption of moisture entering theenvelope.

5. A flash lamp as set forth in claim 1 wherein the said deliquescentsubstance comprises a hydrate which has a white porous appearance in itsanhydrous solid state and turns water clear upon absorption of moistureand transformation into its hydrated liquid state.

6. A flash lamp comprising a hermetically sealed lighttransmittingenvelope interiorly free of moisture, a lamp mount structure sealed insaid envelope, a light-giving charge in said envelope, acombustion-supporting gaseous filling in said envelope, and a quantityof anhydrous lithium bromide located in said envelope on said mountstructure.

7. A flash lamp comprising a hermetically sealed lighttransmittingenvelope interiorly free of moisture, a lamp mount structure sealed insaid envelope, a light-giving charge in said envelope, acombustion-supporting gaseous filling in said envelope, and a quantityof anhydrous strontium perchlorate located in said envelope on saidmount structure.

References Cited in the file of this patent UNITED STATES PATENTS

